Heat generated through different energy forms is used inter alia in the field of hyperthermia, which involves the treatment of tissues of different kinds with the supply of heat. Hyperthermia is particularly used for the treatment of malign tumors, whereby one makes use of the fact that certain cancer cells are destroyed at a certain temperature, for example about 42.degree. C., whereas surrounding healthy cells remain unaffected at this temperature. Hyperthermia is also used in the treatment of certain benign conditions of disorder, for example prostate hyperplasia (BPH), where heating of the swollen prostate rectally or urethrally to a temperature range of about 44.degree.-48.degree. C. gives a certain positive effect, probably depending on the fact that the swelling is reduced.
Heat is utilized also medicinally in that laser beams or instruments heated by radio frequency are introduced at certain surgical operations, the tissue being burned at the same time as the blood of surrounding vessels is brought to coagulate in this manner also certain organ parts showing large flow of blood (perfusion) are treated.
A pronounced problem in hyperthermia resides in measuring and controlling the temperature in the tissue to be treated so as not to destroy surrounding healthy tissue. This is particularly the case with deeply located tissues or organs. Irrespective of the manner at which heat is treated, such as by heat conduction or through ultrasound, radiofrequent energy, microwaves, differences in the structure and flow of blood of the tissue contributes to difficulties with regard to maintaining a certain temperature or obtaining a certain depth of treatment.
The choice of method of treatment is affected by these factors and it is thus for example not possible to establish a desired temperature level by means of heat conduction from a heat source in view of the fact that the temperature drop inwardly through the tissue becomes too large depending on the cooling effect of the blood. The temperature distribution in different parts of the treated organ also often becomes uneven in view of variations in the flow of blood. Also in the treatment of more deeply penetrating methods, for example using radio frequency techniques in the frequency range up to 300 MHz or microwave techniques in the frequency range 300-2450 MHz, varying blood perfusion raises problems, partly in view of the fact that the temperature gradient inwardly in the tissue varies, partly through the fact that the temperature will vary within different parts of tissue.
As indicated above also temperature measurement constitutes a problem. It is often impossible to measure the temperature at a sufficient number of locations in the tissue volume to be treated, a condition which is aggravated by varying perfusion which results in a need of an even larger number of measuring locations.
It has been suggested in the treatment of certain tumors to introduce by operation metal needles at a certain distance from each other, said needles being made of a ferromagnetic material are capable of heating wirelessly through magnetic induction. This technique means that the needles are left for a number of treatments and in each treatment the patient is placed so that an exterior induction coil surrounds the part of the body containing the tumor involved. This coil generates a magnetic field, the intensity and strength of which affects the heat released from the needle by heat conduction. By selecting a metallic material among certain alloys having such magnetic properties as to have a so called Curie point corresponding to the desired temperature no particular thermoelements for measuring the temperature are required. Such needles of so called ferromagnetic alloys operate as if had they a built-in thermostate and also generate during the heating phase less heat the closer one comes to the desired temperature (the Curie point). The absence of equipment for temperature measurement and temperature control is, of course, a great advantage, but the drawback of this particular technique is the fact that the needles have to be capable of producing sufficient quantities of energy so as to reach the desired treatment temperature. On the other hand the needles must not be too thick or must not flex too easily, and therefore the technique is not suitable for application on organ parts where the blood perfusion is high or uneven. Another drawback associated with the technique is that it cannot be applied to the treatment of difficultly accessible tumors or intra-cavitarily.
Heat treatment has also been applied to excessive uterus hemorrhage (menorrhagia), which disorder shows very strong bleeding as a symptom. The most common measure adhered to at this disorder is uterus extraction, which is a traumatically very large surgical operation associated with certain risks and which also can result in conditions of psychical stress. Only in the United States about 0.5 million of hysterectomies are made, the majority thereof because of menorrhagia.
For a long time one has tried to develop methods for the suitable treatment of the disorder, inter alia by destroying the uterus mucosa (endometrium) by heating, for example using a laser, but this is time consuming and requires pronounced caution and skill. Attempts using microwave heating have not been very successful, since the uterus cavity is flattened and triangular shaped and the distribution of the microwaves is such as to result in a very uneven treatment. The large flow of blood in the endometrium surrounding the myometrium also results in large temperature drops in view of the cooling effect of the blood, resulting in uneven heating. There are also difficulties to protect the cervix and the vagina from burns. Moreover, experience shows that perforation of the uterus wall can take place with the treatment using a laser.
Examples illustrating prior art concerning the treatment of internal disorders while supplying heat and optionally supplying pressure are found in U.S. Pat. Nos. 4,160,455, 4,773,899, 4,799,479, 4,709,698 and 4,949,718, and the EP-application, publication No. 0 370 890 A1.
The present invention has for its purpose to provide new techniques for carrying out hyperthermia, whereby the drawbacks of the prior art are eliminated or at least substantially reduced.
One particular object of the present invention is thus to provide a device for carrying out such so called hyperthermia in a body cavity or duct in a manner which is satisfactory from a safety point of view. For these and other objects the device according to the invention includes a distal section intended to be inserted into said cavity or duct comprising a centrally located, heat-releasing element, which is either surrounded by an elongate housing or is itself constituted by an elongate housing, and a flexible and/or elastic enclosure surrounding said housing in a liquid-tight manner, further including means for supplying energy to the heat-releasing element and an axially operating inlet passage at the proximal part of the housing, an outlet from the housing being arranged for the supply of heat-transmitting medium under pressure for expansion of the flexible enclosure to accomodate to said cavity or duct and to exert a con%rolled pressure on surrounding walls. The device according to the invention further comprises a second inlet to the housing and means for internal circulation of said medium through the housing, the heat-releasing element being of an inherently self-regulating type.
As will be explained later in this disclosure heat-releasing elements of the inherently self-regulating or self-controlling type are exemplified by materials of the PTC-type, or by ferromagnetic materials where the means for the supply of energy are based on magnetic induction.
The PTC-material is a semiconductor and has a constant resistance up to a specific temperature, the so called Curie Point (CP) or trip point (TP), which is predetermined. At the trip point, the resistance increases by 100% but over this temperature the resistance increases drastically, for example 20-30% per. .degree. C.
When the material is connected to an electric source of a certain voltage it will emit energy in form of heat from its surfaces in such a way that the larger the surface the greater the emission will be. Because of the temperature-depending resistance, it is self-regulating with regard to heat emission at temperatures in the range of the TP, e.g. the material is capable of maintaining steady state conditions even if variations in power requirement occur at a certain temperature level.
An element containing a ferromagnetic material having a CP is also self-regulating and the material will, at a certain predetermined temperature close to the CP, cease to be ferromagnetic, and thus placed in a magnetic-field the energy emission will be drastically reduced.
According to the invention, the centrally located heating element consists of a self-regulating material of a compact design enabling access to the treatment site but at the same time providing sufficient heat-emitting surfaces to be capable to emit sufficient energy at a certain temperature level even at variations in power.
The problem of creating sufficient power output while avoiding self-inhibition associated with a compact design of the heating element has been solved in accordance with the invention by arranging the compact heat releasing self-regulating material in a surrounding elongate housing or by designing the material itself as an elongate housing with an inlet and an outlet, the heat-transmitting medium being forced through and around the material by an efficient internal circulation. Inspire of restriction in size the material can provide for sufficient power output at temperatures in the range of TP or CP, thus resulting in successful treatment under self-regulating conditions. This also means that the heat-emitting element above the predetermined temperature range of CP operates in such a manner that the energy-generation automatically will be significantly reduced and self-inhibition will occur so that overheating thereby cannot take place under any circumstances.
For the treatment of disorders of the uterus the material of the heat-releasing element may have a trip point or Curie point lying within the range about 60.degree. C. to about 90.degree. C., particularly about 70.degree. C. to about 80.degree. C. On the other hand, for the treatment of prostatic disorders said ranges may be from about 45.degree. C. to about 65.degree. C., particularly about 48.degree. C. to about 56.degree. C.
In accordance with a preferred embodiment of the invention the device contains in said elongate housing two or several, axial and parallelly arranged part-elements of PTC-type having substantially parallel surfaces. Said part-elements are suitably placed spaced from each other and from the surrounding housing wall to form canals or passages between and about the part-elements to form sufficient surface and to provide for effective and even heat-emission to the surrounding flowing heat-transmitting medium.
In order to obtain a sufficient power output the PTC-material is preferably arranged with a packing degree within said housing within the range about 35 to about 70% by volume, i.e. corresponding to a void volume of about 65 to about 30%, preferably about 45 to 65% by volume, i.e. corresponding to a void volume of about 55 to about 35%.
In such preferred embodiment the thickness of the part-elements is suitably at most about 1.5 mm and they may have a power capacity at steady state of at least about 1-1.5 W/cm.sup.2 of exposed element surface at a voltage of about 24 V. In this disclosure the expression "exposed element surface" refers to the total surface of the heating element exposed to the heat-transmitting medium. Due to the lower electrical resistance at temperatures below the self-regulating temperature range the emitted power will be much higher, such as 3 times higher than at steady state, which is of a great advantage since it significantly reduces the start-up time.
For use in narrow passages in a living body said housing preferably has an outer diameter of at most about 7-8 mm, and at such dimension its capacity of heat-generation at steady state shall correspond to a release of heat of about 3 W/cm axial length or extension of the housing at the treating temperature used and at a voltage of about 24 V.
It is preferred that said means for internal circulation has a capacity at steady state conditions of replacing the void volume of the housing of said medium at least about 30 times per minute, and preferably at least about 60 times per minute.
According to an alternative embodiment of the invention said elongate housing may be constituted by a cylindrical element of PTC-type which is flown through and around by the heat-transmitting medium.
According to a particularly preferred embodiment of the invention the device may contain an inlet for the medium located in the housing on the opposite side of element relative to said outlet, and means for imparting flow to the medium in an internal circuit from the space between housing and the surrounding flexible enclosure, through housing via said inlet and outlet, for absorbing heat and through the space between housing and enclosure for the release of heat through the enclosure wall.
In such embodiment of the invention the device may be characterized by at least one first back valve arranged in association with the inlet, said back valve allowing flow into the interior of the housing, and the flow resistance of which in an open position is lower than the flow resistance through the housing, said means for the flow of the medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of the pressurized quantity of medium enclosed in the inlet canal of the device after expansion of the enclosure, whereby the inlet is closed and the outlet is open, whereby the circulation of the medium in a circuit is provided.
According to yet another embodiment of the invention the device is characterized by at least one first back valve arranged in association with the outlet allowing flow out of the interior of the housing, the flow resistance of the inlet being higher than the flow resistance through the housing, said means for the flow of the medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of the pressurized medium enclosed in the inlet canal of the device after expansion of the enclosure, whereby the inlet is open and the outlet is closed, thereby providing circulation of the medium in a closed circuit.
According to an alternative embodiment of the invention the device is characterized by an inlet for the medium arranged in the housing on the other side of the element relative to said outlet and by a partition placed between said inlet and the element or between said element and the outlet, respectively, forming a chamber and which is provided with an axial passage containing a second back valve, which is oppositely placed relative to the first back valve placed in the inlet, the means for the flow of the medium in an internal circuit being arranged to provide a reciprocating movement of a small quantity of the pressurized medium enclosed in the inlet canal of the device after expansion of the enclosure, whereby the inlet is closed and the outlet is open or the inlet is open and the outlet is closed, respectively, thereby providing circulation of the medium in a closed circuit.
It is preferred in the device according to the invention to provide two oppositely placed back valves in connection with the inlet and the outlet. Said partition is suitably placed between the inlet and the element.
The back valves used in association with the present invention can be of any conventional type. As examples there may be mentioned flap valves, ball valves, disc valves, etc. Flap valves are preferred in view of their simple design.
Said means for providing flow of the medium may, in accordance with a preferred embodiment of the invention, be arranged to provide for a volumetric flow of the medium. Such means may comprise a reciprocating piston.
According to an alternative embodiment of the device according to the invention said means for the flow of the medium in an internal circuit include a propeller or an axial pump wheel placed between the radial inlet and outlet.
As an alternative, to provide for circulation of the medium the device according to the invention may contain means comprising a reciprocating piston provided with one or several axially directed apertures and corresponding back valves.
In another embodiment of the device according to the invention said distal section comprises a central tubular element and a number of parallel, longitudinally extending bars, bands or wires of a ferromagnetic material essentially evenly distributed around said tubular element and constituting said means for heat generation. The metal alloy used suitably essentially consists of nickel and copper, nickel and silica, iron and platinum or iron and palladium.
In such an embodiment the device includes means for the supply of energy comprising an induction coil intended to surround the body or body part containing said body cavity or duct. It is preferred that the ferromagnetic material has substantial extension in the direction of a magnetic induction field. To obtain the necessary power output from the compact element the ferromagnetic material is suitably designed with a packing degree lying within the range about 25 to about 60%, i.e. corresponding to a void percentage of about 40 to about 75% by volume.
Also as indicated above, the device according to the invention is particularly suited for the treatment of disorders in uterus, for example menorrhagia. Alternatively, the device according to the invention can be used for the treatment of prostatic disorders.
The invention also includes a method for carrying out so called hyperthermia in a body cavity or canal, i.e. with the supply of heat to said body cavity. Such hyperthermia is carried out with simultaneous application of a controlled pressure against the tissue surrounding the body cavity. This method is characterized by the fact that the supply of heat is provided by using a heat-releasing system of a self-controlling or self-regulating type. As previously mentioned the method is particularly suited for the treatment of disorders in the uterus or in the prostate.
In connection with the use of a self-regulating system containing a semiconductor material of PTC-type is particularly preferred from a safety point of view to feed the semiconductor material using a low-voltage current, for example having a voltage of at most about 50 V and particularly at most about 30 V. Using available semiconductor materials of PTC-type even lower voltages can be used, such as down to 20 to 25 V, enabling use of rechargeable batteries. This excludes the risk for electric shocks.